ANALOG ELECTRONIC CIRCUITS
Faculty : Harini Vaikund
Diode Resistance, Diode Equivalent circuits,
transition and diffusion capacitances
Clippers and Clampers, Rectifiers.
UNIT – 2 :
Operating point, analysis and design of
Fixed bias circuits, Emitter stabilized
Voltage divider bias and Collector voltage
Transistor switching circuits. Bias
stabilization: stability factor of different biasing circuits.
UNIT – 3: Transistor Modelling and Frequency
Transistor as two port network, low frequency hybrid model., relation between h– parameter model of CE, CC and
Millers theorem and its dual. General frequency
considerations, low frequency response.
Miller effect capacitance, high frequency response.
UNIT – 4: Multistage, Feedback and Power
a) Multistage Amplifiers: Cascade
and cascade connections,
Darlington circuits, analysis and
b) Feedback Amplifiers:
Feedback concept, different type of
feedback circuits-block diagram
approach, analysis of feedback
c) Power Amplifiers:
Amplifier types, analysis and design
UNIT 5: Oscillators & FET
a) Oscillators: Principle of operation, analysis of phase shift oscillator, Wien bridge
oscillator, RF and crystal oscillator. (BJT versions)
b) Field Effect Transistors: Construction, working and
characteristics of JFET and MOSFET. Biasing of JFET. Analysis and design
of JFET (only common source configuration with
❑ Robert L. Boylestad and Louis Nashelsky,
“Electronic Devices and Circuit Theory”,
11th Edition, Pearson Education, 2015.
❑ Millman and Halkias, “Electronic Devices and
Circuits”, 4th Edition, Mc Graw Hill, 2015.
❑ David A Bell, “Electronic Devices and
Circuits”, 5th Edition, Oxford University
Basic Electronics Questions
What are Circuits?
What is the difference between analog and digital circuits?
Why do we need analog and digital circuit?
What are the applications we are using these circuits?
Why do we have to study these as an electrical and electronics engineer?
Where will we be using these in future?
• Application - Home Appliance, Medical Applications, Robotics, Mobile
Communication, Computer Communication etc.
• Atom is the basic building block of all the elements.
• Atom = central nucleus of +ve charge around which –ve charged electrons
• Electrostatic force - attraction between electrons and nucleus which holds
electrons in different orbits.
• Valence electrons - Outermost orbit electrons.
• Free electrons - Valence electrons loosely attached to nucleus.
Basic Electronics• Definite energy - single isolated atom an
electron in any orbit.
• Solids are atoms are brought together, an
atom is influenced by the forces from
• So an electron in any orbit can have a
range of energies rather than single
• Range of energy levels are known as
• Any material there are two distinct energy
bands in which electrons may exist –
Valence band and conduction band.
• Range of energies possessed by valence
electrons is called valence band.
• Range of energies possessed by free
electrons is called conduction band.
• Valence band and conduction band are
separated by energy gap in which no
electrons normally exist this gap is called
• Electrons in conduction band are either
escaped from their atoms (free electrons)
or only weakly held to the nucleus.
• So electrons in conduction band may be
easily moved around within the material
by applying relatively small amount of
energy. (either by increasing the
temperature or by focusing light on the
material etc. )
• This is the reason why the conductivity of
the material increases with increase in
• Classification of materials based on
Energy band theory:
Based on the width of the
forbidden gap, materials are broadly
Classification of Materials
• Conductors are those substances, which
allow electric current to pass through
• Example: Copper, Al, salt solutions, etc.
• In terms of energy bands, conductors are
those substances in which there is no
• Valence and conduction band overlap as
shown for this reason, very large number
of electrons are available for conduction
even at extremely low temperatures.
• Conduction is possible even by a very
weak electric field.
• Insulators are those substances, which do
not allow electric current to pass through
• Example: Rubber, glass, wood etc.
• In terms of energy bands, insulators are
those substances in which the forbidden
gap is very large.
• Thus valence and conduction band are
widely separated as shown therefore
insulators do not conduct electricity even
with the application of a large electric field
or by heating or at very high temperatures.
• Semiconductors are those substances whose
conductivity lies in between that of a
conductor and Insulator.
• Example: Silicon, germanium, Cealenium,
Gallium, arsenide etc.
• Energy bands, in semiconductors the
forbidden gap is narrow. Thus valence and
conduction bands are moderately separated
• Valence band is partially filled, the
conduction band is also partially filled, and
the energy gap between conduction band
and valence band is narrow.
◦ Comparatively smaller electric field is
required to push the electrons from valence
band to conduction band . At low
temperatures the valence band is
completely filled and conduction band is
completely empty. Therefore, at very low
temperature a semi-conductor actually
behaves as an insulator.
• Free electrons in the conduction band are moved
under the influence of the applied electric field.
• Since electrons have negative charge they are
repelled by the negative terminal of the applied
voltage and attracted towards the positive
• Hole transfer involves the movement of holes.
• Holes may be thought of positive charged
particles and as such they move through an
electric field in a direction opposite to that of
Semiconductor◦ In a good conductor (metal) – the current
flow is due to free electrons only.
◦ In a semiconductor as shown - the current
flow is due to both holes and electrons
moving in opposite directions.
◦ The unit of electric current is Ampere (A)
and since the flow of electric current is
constituted by the movement of electrons in
conduction band and holes in valence band,
electrons and holes are referred as charge
Classification of semiconductors:
a) Intrinsic semiconductors.
b) Extrinsic semiconductors.
Intrinsic SemiconductorIntrinsic semiconductors:
A semiconductor in an extremely pure form is
known as Intrinsic semiconductor.
• Example: Silicon, germanium.
• Both silicon and Germanium are tetravalent
(having 4 valence electrons).
• Each atom forms a covalent bond or
electron pair bond with the electrons of
At low temperature
• At low temperature, all the valence electrons
are tightly bounded the nucleus hence no
free electrons are available for conduction.
• The semiconductor therefore behaves as an
Insulator at absolute zero temperature.
Crystalline structure of Silicon (or Germanium)
Intrinsic SemiconductorAt room temperature
◦ Some of the valence electrons gain enough
thermal energy to break up the covalent
bonds.This breaking up of covalent bonds
sets the electrons free and is available for
◦ When an electron escapes from a covalent
bond and becomes free electrons a vacancy
is created in a covalent bond as shown.
Such a vacancy is called Hole. It carries
positive charge and moves under the
influence of an electric field in the direction
of the electric field applied.
◦ Numbers of holes are equal to the number
of electrons since; a hole is nothing but an
absence of electrons.
Crystalline structure of Silicon (or Germanium) at room
• When an impurity is added to an intrinsic semiconductor its conductivity changes.
• This process of adding impurity to a semiconductor is called Doping and the impure
semiconductor is called extrinsic semiconductor.
• Depending on the type of impurity added, extrinsic semiconductors are further classified
• n-type semiconductor.
• p-type semiconductor.
◦ When a small current of Pentavalent impurity is
added to a pure semiconductor it is called as n-
◦ Addition of Pentavalent impurity provides a large
number of free electrons in a semiconductor
◦ Typical example for pentavalent impurities are
Arsenic, Antimony and Phosphorus etc. Such
impurities which produce n-type
semiconductors are known as Donor impurities
because they donate or provide free electrons to
the semiconductor crystal.
• Due to thermal energy, still hole electron pairs
are generated but the number of free electrons
are very large in number when compared to
• So in an n-type semiconductor electrons are
majority charge carriers and holes are minority
charge carriers .
• Since the current conduction is pre-dominantly
by free electrons( -vely charges) it is called as n-
type semiconductor( n- means –ve).
Energy band diagram for n-type semiconductor
◦ When a small amount of trivalent impurity
is added to a pure semiconductor it is called
◦ The addition of trivalent impurity provides
large number of holes in the semiconductor
◦ Example: Gallium, Indium or Boron etc.
Such impurities which produce p-type
semiconductors are known as acceptor
impurities because the holes created can
accept the electrons in the semi conductor
◦ Due to thermal energy, still hole-electron
pairs are generated but the number of holes
is very large compared to the number of
◦ Therefore, in a p-type semiconductor holes
are majority carriers and electrons are
◦ Since the current conduction is
predominantly by hole( + charges) it is
called as p-type semiconductor (p means
Energy band diagram for p-type semiconductor
PN Junction Diode
PN Junction Diode:
• When a p-type semiconductor material is suitably joined to n-type semiconductor the contact
surface is called a p-n junction.
• The p-n junction is also called as semiconductor diode.
Applications of diode:
• Used as rectifier diodes in DC power suppliers
• Used as clippers and clampers
• Used as switch in logic circuit in computers
• Used as voltage multipliers.
Construction and working of a PN Junction diode Open Circuited PN Junction:
• p-type semiconductor having –ve acceptor
ions and +vely charged holes.
• n-type semiconductor having +ve donor
ions and free electrons.
• Two pieces are suitably treated to form pn
junction, then there is a tendency for the
free electrons from n-type to diffuse over to
the p-side and holes from p-type to the n-
side . This process is called diffusion.
• As the free electrons move across the junction from n-type to p-type, +ve donor ions are uncovered.
• Hence a +ve charge is built on the n-side of the junction. At the same time, the free electrons
cross the junction and uncover the –ve acceptor ions by filling in the holes.
• Therefore a net –ve charge is established on p-side of the junction.
Construction and working of a PN Junction diode
• When a sufficient number of donor and
acceptor ions is uncovered further diffusion
• Thus a barrier is set up against further
movement of charge carriers. This is called
potential barrier or junction barrier.
• The potential barrier is of the order of 0.1
• Outside this barrier on each side of the
junction, the material is still neutral.
• Only inside the barrier, there is a +ve
charge on n-side and –ve charge on p-side.
This region is called depletion layer.
Biasing of a PN junction diode:
Connecting a p-n junction to an external DC voltage
source is called biasing.
1. Forward biasing
2. Reverse biasing
PN Junction – No Bias (V = 0)
• Absence of external voltage across the p-n
junction is called the unbiased diode.
• Because of the density gradient electrons and
holes diffuse and they combine leaving the ions
unneutralised and are called uncovered charges.
• The uncovered charges generate an electric field
directed from n-side to p-side called as barrier
field which opposes the diffusion process
• Since the vicinity of the junction is depleted of
mobile charges. Hence called a as depletion
PN Junction – Reverse Bias (VD<0V)• Positive polarity of the external bias VD is
connected to n-type and negative terminal is
connected to p-type.
• The number of uncovered positive and negative
ions will increase in the depletion region causing
widening the depletion region which creates a
great barrier for the majority carrier to overcome,
effectively reducing the majority carrier flow to
zero and hence the current due to majority
• The minority carriers which travels down the
potential barrier remain unaffected and give a
small current called the reverse saturation
current denoted as Is.
PN Junction – Forward Bias (VD >0V)• Positive polarity of the external bias VD is connected
to p-type and negative terminal is connected to n-
• External bias VD exerts a force on the mobile carriers
to move them towards the junction. At the boundary
they recombine with the ions and reduce the width of
the depletion region.
• The depletion region will continue to decrease in
width as the voltage is increased further and a heavy
flood of electrons will move from n-side to p-side
giving the Imajority an exponential rise from p-side to
• The minority carrier flow will not be affected by this
because the conduction level is determined by the
limited number of impurities in the material and the
current is denoted by Is.
◦ The total current is given by
ID=IForward+IReverse =Imajority - Iminority
◦ In terms of reverse saturation current, ID
can be written as
ƞ𝑲𝑻-1)) is called the
Where e- Charge of an electron
T-Temperature in Kelvin
η- Quality factor depends upon the
diode material (η=2 for Si and 1 for Ge)
𝑽𝑫- Supplied voltage across the
Breakdown ConditionZener Breakdown
• Too much of reverse bias across a p-n junction exert a
strong force on a bound electron to tear it out from the
• Thus a large number of electron and hole pair will be
generated through a direct rupture of the covalent bonds
and they increase the reverse current and gives sharp
increase in the characteristics. It is called zener
• Diode employing the unique portion of the characteristics
of a p-n junction is called zener diode.
• Maximum reverse voltage potential that can be applied
before entering the zener region is called the peak inverse
voltage (PIV) or peak reverse voltage (PRV).
Avalanche Breakdown:• With increasing reverse bias voltage,
the electric field across the junction
of a diode increases.
• At a certain value of the reverse
voltage, the electric field imparts a
sufficiently high energy to a thermally
• The carrier on colliding with an ion
on its way disrupts a covalent bond
and gives a new hole electron pair.
• This process is cumulative and gives
an avalanche of carriers in a very
short time. It is called avalanche
Diode Resistance DC or Static Resistance
• The application of a dc voltage to a circuit containing a semiconductor diode will result in an operating
point on the characteristic curve that will not change with time.
• The resistance of the diode at the operating point can be found simply by finding the Corresponding
levels of VDand ID
• The dc resistance levels at the knee and below will be greater than
the resistance levels obtained for the vertical rise section of the
characteristics. The resistance levels in the reverse-bias region
will naturally be quite high. Since ohmmeters typically employ
a relatively constant-current source, the resistance determined
will be at a preset current level (typically, a few mill amperes).
•DC or Static Resistance
•AC or Dynamic Resistance
Determining the dc resistance of a diode at
a particular operating point
AC or Dynamic Resistance
• Static resistance that the dc resistance of a diode is independent of
the shape of the characteristic in the region surrounding the point
• If a sinusoidal rather than dc input is applied, the situation will
• The varying input will move the instantaneous operating point up
and down a region of the characteristics and thus defines a specific
change in current and voltage.
• With no applied varying signal, the point of operation would be the
Q-point appearing on figure determined by the applied dc levels.
• The designation Q-point is derived from the word quiescent, which
means ―still or unvarying.
• A straight line drawn tangent to the curve through the Q-point will
define a particular change in voltage and current that can be used to
determine the ac or dynamic resistance for this region of the diode
Defining the ac resistance of a diode
• If the input signal is sufficient enough to produce a large swing,
then the resistance related to the diode for this region is called as AC
• It is determined by the straight line that is drawn linking the
intersection of the minimum and maximum values of external input
Average AC Resistance
Diode Equivalent Circuits
• Equivalent circuit is a combination of element properly chosen to best represent the actual
terminal characteristics of a device or system in a particular operating point.
• Diode replaced by equivalent circuit in many practical electronic circuits for analysis purpose.
• Such equivalent circuit is called circuit model.
• Methods of replacing diode by circuit model
• Piecewise-Linear Equivalent Circuit : One technique for obtaining an equivalent circuit for a diode is
to approximate the characteristics of the device by straight-line segments. The resulting equivalent
circuit is naturally called the piecewise-linear equivalent circuit.
• Simplified Equivalent Circuits:
• Ideal Equivalent Circuits